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NEED HELP! 3000W electric bike battery set up

3587 Views 30 Replies 7 Participants Last post by  Solarsail
hi to all!

i'm trying to build a DIY 18650 battery pack out of the samsung INR 3500mahs and my configuration is 23 in parallel and 30 in series = 100Ah 96V. my confusion is on charging this beast. what is a good charger that doesn't blow up the battery pack but can charge it quickly.

Any inputs on this set up would be much appreciated!


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Perhaps the 4200 watts is output power and the motor is only 4200/6240 = 67% efficient when producing this peak output?
YES. Thats what i was thinking but i wasn't sure so i did double check with the seller and turns out output power is 4200 and input is 6240.

heres the link to the motor i was going for:

i wanted to something to go 100km/h easy but the efficiency seems pretty terrible at high speed...

what motors do you suggest based on the 100km/h preference?
im thinking of sticking with the 4 modules with separate charging ports and chargers. right now im looking at the batteries to do this job.. what do you suggest? i found these which are relatively cheap and hold high capacity ( ). i want to have a high range but also use a motor that can push to 100km/h or so without paddling. as always, open to more suggestions and advice. thanks!
Whoa ... I thought by e-bike you were building an electric motorcycle. But it seems you are building an electric bicycle. If so, why so much capacity, and how do you intend to carry the pack?

A 26s30p pack will be about 10 kWh. That is a range of almost 1,000 kilometers! Do you need so much range?

A bicycle travels anywhere from 70 km to 125 km /kWh. A moped goes about 37 km/kWh. A motorcycle about 25 km/kWh.

High capacity 18650 batteries are about 4 kg/kWh. With 20% overhead for the enclosure, cabling, electronics, your pack will weigh 50 kg! Can the bike even carry this? And the size of the pack can be 25 to 30 liters.

Do you really plan to travel 100 kph on a bicycle?
Those are very good batteries. They are much cheaper in China (about $3 a piece) but add $1.1 for air freight. See my project:
theres enough space on the bike, its a pretty big 28' xl frame but 1000km?!!! I think i messed up the math by alot then lol.

i did this:
65A peak current
96V motor
so, 65A x 96V = 6240w --> peak motor input. the output power is 4200w (based on what i was told by the seller)

my battery is 96V x 100ah =9600wh
9600wh/6240w= 1.54 hours of riding 120km/h

which means 120km/h x 1.54 = 184.6 km at max speed.

i live pretty far from the city ( about 30km ) so it would be nice to do 120km/h on the highway with a heavy bike :D.

Correct the math if im wrong (which i think is 100% wrong at this point :D)
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At 120 kph, the unit range of km/kWh will drop drastically due to aerodynamic drag, and motor inefficiency, and friction etc. Even if it drops to 30 km/kWh, you are still at nominal:

96V * 3.5Ah * 30p * 30(km/kWh) / 1000 = 300 km range.

But you can't drive the whole way at that speed. Let's say you drive 1/3 at 20 kph, 1/3 at 60 kph, and 1/3 at 100 kph. The respective ranges are let's say 80, 65, 30 km/kWh for an average of 58 km/kWh.

So your range will be 585 km - still too high. I would suggest a range of 150 km, to make the pack as light and small as possible. So the p becomes:

150 * 1000 / (96 * 3.5 * 58) = 8 in parallel. Since the 3.5 is really a 3.3, and the 96 is really a 93.6, and in practice the 58 becomes a 50, and add a 10% margin, you need:

1.1 * 150km * 1000 / (26 * 3.6V * 3.3Ah * 50km/kWh) = 11 cells in parallel

I.e. two modules of 13s11p. You are down from 50 kg (110 lbs) to 17 kg. Much more manageable.

Note that the 150 km range includes high speed runs. If you were to travel 40 kph uniformly, your range will be about 225 km.
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4200W is an awful lot of power. In steady state riding on level ground at 100 kph, you will never use this kind of power. The 4200 peak power may be reached during abrupt acceleration or steep hill climbing. An automobile running at that power will probably do 45 - 50 kph.

When the manufacturer says 65A peak, it means that is what the controller and motor can handle. It does not mean it will handle it at 96V. As the power requirement approaches 4200W maximum power, then add the motor and controller inefficiencies (10% at such high power and 10% respectively), and you need 5,100W. But what if your battery are almost empty at 3.0V each? Then the amount of current you must draw becomes

5,100W / (26 * 3.0V) = 65A. So your controller and motor can handle that at a lower voltage. But when hill climbing on full batteries, it is using only 5100/(26*4) = 49A.

It does not mean that at 120 kph you will need all the 4200W. Just ask the seller what the power requirement is for 100 kph on level ground no acceleration. I have assumed 30 km/kWh at this speed. So output power is 100km/h / 30km/kWh = 3,300W or 1.21*3300/(26*3.6) = 43A input current. Even this is quite conservative, and I think it will be much lower, depending on aerodynamics. Normal bicyclist output on level ground at let's say 30 kph is 100W. So using the square law, it should be (100/30)^2 * 100 = 1100W output power at 100 kph, or 1,350W input.

Maybe the motor or controller is not very efficient. Which means at those powers, it will be generating so much heat that it will probably burn up.
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This 600km range setup seems PERFECT! im a range anxious person and i dont mind the extra weight and space taken by the batteries (i have enough space in the bike frame). so if i were to build 2 chargers to push 25A for each 2 pairs(13s14p).. what do i need?

i found thess 2 power supplies on ali :

and this charger module:

Do you use an AC plug wired to the power supply and power supply wired to the charger module ? How does this work? what else do i need ? Thanks!
I am about to write up the charger section for my project which I gave you the link. Keep on checking on it, till I make the post.

You need 1) power supply, 2) charger, 3) PMC (protection-balance). Also optionally switches, fuses, ammeter, voltmeter, plugs and jacks.

I use a 800W 48Vx16.7A supply, for a module. This will be set to 46 to 51V.

Charger I use is 1200W, 20A, but will be running at 800W. It is CCCV and is isolated. This will be set to 54.0V exactly (4.15V per cell for longevity). Charging will be set at 1.5A per cell. May increase it later. Li-ion chargers must be CCCV - no exception.

PMC I have already posted link.

The charger module you linked is not suitable because it is not CCCV. And its power is no good. Doesn't even say what is the power. My guess is it is not more than 4A at 54V, which means it will take 12 hours to charge one module. It is meant for Lead Acid. I already posted a link to a 900W CCCV charger with digital display.

Yes, AC goes to power supply, which then goes to the charger, which then goes to the - of group 1 and + of group 13. - of group 1 should obviously NOT be connected to chassis. The - of group 1 also goes to the PMC which can cut it off, and from PMC comes out of the module to be the module - (not to be grounded to chassis). This is then connected to the - of the parallel module. Then if the pair is the upper half, the minus goes to the + of the lower modules. If it is the lower half, then it goes to the controller.

Note: each cell should also have its own little fuse (a thin wire). I believe e-bike pack makers omit this.
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I only read through a few of the first responses.. some get wordy!

I saw one guy mentioned getting a 124V charger, smart to not charge them all the way to 100%. Your cells will still become unbalanced over time, so a top balancing BMS that balances when you charge is really the minimum you need. Here is one that does 30S

Is it going to be somewhat confusing to make work correctly? Sure.. but not impossible. These cheap Chinese BMS' seem to work just fine and are really all that is required so long as you aren't continually draining your pack under ultra high amperage OR draining it down extremely far. SO in summation:

get a charger that outputs somewhere around 120V, watch pack voltage high/low and balance charge it. Good to go!
get a charger that outputs somewhere around 120V, watch pack voltage high/low and balance charge it. Good to go!
Thanks, but the link is to a LiFePO4 BMS. Will not work with Lico.
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